a) Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus and method, and more particularly to a semiconductor manufacturing apparatus and method for generating plasma and processing the surface of semiconductor substrate.
b) Description of the Related Art
Various processes using plasma are widely applied to manufacture of semiconductor devices. However, if wafers are directly exposed to plasma, they are damaged.
An example of a conventional barrel type plasma processing system will be described with reference to FIGS. 10A and 10B.
FIG. 10A is a schematic perspective view of a barrel type plasma processing system. Two electrodes 101a and 101b are disposed on the wall of a cylindrical process chamber 100, the two electrodes facing each other through the process chamber. The electrode 101a is grounded and the electrode 101b is connected to a radio frequency (RF) power source 102.
As an RF voltage is applied between the electrodes 101a and 101b, an RF electric field is generated in the process chamber 100 into which process gas has been introduced. The RF electric field causes the process gas to discharge in a plasma state.
Wafers 103 are exposed to and processed by the plasma. Since the wafers 103 are directly exposed to the plasma, the wafer surfaces are adversely affected by the plasma, which is one of the reasons of lowering manufacture yield.
FIG. 10B is an equivalent circuit diagram of the plasma processing system shown in FIG. 10A. The electrodes 101a and 101b of the barrel type plasma processing system of FIG. 10A form a capacitor 121. An RF power is supplied from an RF power source 122 to the capacitor 121 formed by these electrodes so that capacitively coupled plasma is generated.
The structure and operation of one of conventional coaxial type plasma processing systems will be described with reference to FIGS. 11A and 11B.
FIG. 11A is a schematic perspective view of a conventional coaxial type plasma processing system. An external electrode 111 is disposed surrounding the wall of a cylindrical process chamber 110. A cylindrical internal electrode 112 is coaxially disposed in the process chamber 110. Through holes (not shown) are formed in the wall of the internal electrode 112, to allow gas to be transported between outer and inner spaces of the internal electrode 112 via the through holes. The internal electrode 112 is grounded and the outer electrode 111 is connected to an Rf power source 113.
In a cylindrical space defined between the internal and external electrodes 112 and 111, a gas supply pipe 114 and a gas exhaust pipe 115 are disposed at opposing positions relative to the center axis of the process chamber 110. A plurality of through holes (not shown) are formed in the walls of the gas supply and exhaust pipes 114 and 115 on the side opposite to the internal electrode 112 along the axial direction of the pipes 114 and 115. Process gas is introduced from the gas supply pipe 14 to the inside of the process chamber 110 via the through holes of the wall. The process gas is drawn from the through holes of the gas exhaust pipe 115 and exhausted to the outside of the process chamber 110.
FIG. 11B is a schematic cross sectional view of the plasma processing system shown in FIG. 11A as cut in a plane vertical to the center axis. The internal electrode 112 disturbs a flow of process gas. Therefore, most process gas flows in the circumferential directions indicated by arrows A in a cylindrical space between the inner electrode 112 and process chamber 110, and reaches the gas exhaust pipe 115. As an Rf voltage is applied across the inner and outer electrodes 111 and 112, capacitively coupled plasma is generated in this cylindrical space.
Wafers 116 are disposed in the inner space of the inner electrode 112. Although ions of the plasma generated outside of the inner electrode 112 do not enter the inner space of the inner electrode 112, part of radicals 117 diffuses from the through holes of the inner electrode 112 into the inner space where the wafers 116 are disposed. Diffused radicals react with the surfaces of the wafers 116. Reaction by-products diffuse outside of the inner electrode 112, move along the flow of the process gas, and are exhausted to the outside of the process chamber.
With the coaxial type plasma processing system shown in FIGS. 11A and 11B, an Rf electric field is not applied to the inner space of the inner electrode 112, and plasma is not generated in this inner space. Since the wafers 116 are not directly exposed to the plasma, it is possible to prevent damages by the plasma.
The coaxial type plasma processing system shown in FIGS. 11A and 11B is effective in that wafers are not directly exposed to plasma and are not susceptible to damages. However, a process is performed without using plasma energy so that the process speed lowers as compared to a barrel type plasma processing system. According to the experiments made by the inventors, a process speed by a coaxial type plasma processing system lowered to about a half of a process speed by a barrel type plasma processing system.
With the plasma processing system shown in FIGS. 11A and 11B, radicals reach the surface of a wafer mainly by only diffusion. Therefore, if a space between wafers is narrowed, radicals become difficult to reach the wafer surface so that a process speed is lowered. For example, with a gap between wafers being set to 9.52 mm, a plasma ashing rate was 90 nm/min, whereas with a gap between wafers being set to 4.76 mm, it lowered to 30 nm/min. A plasma etching rate also lowers if a gap between wafers is narrowed.